Dissimilatory Arsenate Reduction and In Situ Microbial Activities and Diversity in Arsenic-rich Groundwater of Chianan Plain, Southwestern Taiwan

Abstract

Although dissimilatory arsenic reduction (DAsR) has been recognized as an important process for groundwater arsenic (As) enrichment, its characterization and association with in situ microbial activities and diversity in As-rich groundwater is barely studied. In this work, we collected As-rich groundwater at depths of 23, 300, and 313 m, respectively, from Yenshui-3, Budai-Shinwen, and Budai-4 of Chianan plain, southwestern Taiwan, and conducted incubation experiments using different electron donors, acceptors, and sulfate-reducing bacterial inhibitor (tungstate) to characterize DAsR. Moreover, bacterial diversity was evaluated using 454-pyrosequencing targeting bacterial 16S rRNAs. MPN technique was used to enumerate microorganisms with different in situ metabolic functions. The results revealed that DAsR in groundwater of Chianan plain was a biotic phenomenon (as DAsR was totally inhibited by filter sterilization), enhanced by the type of electron donor (in this case, lactate enhanced DAsR but acetate and succinate did not), and limited by the availability of arsenate. In addition to oxidative recycling of As(III), dissolution of As(V)-saturated manganese and iron minerals by indigenous dissimilatory Mn(IV)- and Fe(III)-reducing bacteria, and abiotic oxidation of As(III) with Mn(IV) regenerated As(V) in the groundwater. Sulfate-respiring bacteria contributed 7.4 and 28.2 % to the observed DAsR in groundwater of Yinshui-3 and Budai-Shinwen, respectively, whereas their contribution was negligible in groundwater of Budai-4. A noticeable variation in dominant genera Acinetobacter and Bacillus was observed within the groundwater. Firmicutes dominated in highly As-rich groundwater of Yenshui-3, whereas Proteobacteria dominated in comparatively less As-rich groundwater of Budai-Shinwen and Budai 4.

Contrasting the Genetic Patterns of Microbial Communities in Soda Lakes with and without Cyanobacterial Bloom

“…The waters of the studied lakes have high As content, with values ranging from 0.05 to 0.5 mg⋅L -1 , mostly found in the form of arsenate – As(V), and the As content being higher in Salina Verde than Salina Preta ( Barbiero et al, 2007 ). The transformation of As(V) (lower toxicity/lower bioavailable) to As(III) (higher toxicity/higher bioavailable) is favored by alkaline conditions, occurring through two main mechanisms: (i) the resistance mechanism (As detoxification efflux system), and (ii) the dissimilatory arsenate reduction, which is predominant under anoxic conditions ( Oremland et al, 2004 ; Kulp et al, 2006 ; Das et al, 2016 ). The mechanism of dissimilatory arsenate reduction was only poorly mapped in our metagenomes, likely because this is a metabolism that takes place in the sediment of these lakes.…”

Microbial community structure in aquifers associated with arsenic: analysis of 16S rRNA and arsenite oxidase genes

“…Agricultural and residential areas possibly contributed to the high abundance of Acinetobacter in groundwater of Rayong province, Thailand (Sonthiphand et al, 2019). In addition, Acinetobacter were commonly detected in As-contaminated groundwater where contributed to arsenic transformations (Das et al, 2016;Li et al, 2015a). Massilia were the dominant taxa found in As-contaminated groundwater of Hetao Basin in China (Li et al, 2013) and in a fermentation system, capable of the degradation of rice bran (Hou et al, 2019).…”

Genome mining, phylogenetic, and functional analysis of arsenic (As) resistance operons in Bacillus strains, isolated from As-rich hot spring microbial mats

“…Due to the toxicity of this metalloid in the environment, it is important to investigate the genetic mechanisms behind the biotransformation processes of arsenic found in microorganisms, such as bacteria (Oremland and Stolz, 2003). Particularly, the Firmicutes are common inhabitants of aquatic systems, such as groundwater or hot spring microbial mats, where elevated concentrations of As constrain the survival of other bacterial species (Das et al, 2016; Prieto-Barajas et al, 2017; Zhang et al, 2020; Oremland and Stolz, 2003). Therefore, it is relevant to find out about the resistance mechanisms of this group of bacterial species that allows them to colonize and permanently be part of such microbial communities.…”